The present invention relates to power wrenches, and more specifically to a combination to power tongs for making up and breaking out threaded connections between adjoining tubular members. In particular, the invention relates to an assembly for gripping and rotating a first threaded tubular member into or out of a second tubular member which is secured against rotation.
Oil field tubular members, i.e. drill pipe and casing, are employed in sections which are joined together at their ends by threaded connections. Power tongs of the type herein described are utilized to make up and break out these threaded connections by securely gripping one tubular member and rotatably driving that member relative to the adjoining member.
In many situations, the adjoining member is not of a sufficient weight, nor attached to a sufficient number of other tubular members to preclude its rotation in response to the rotatably driven tubular member, thereby precluding a complete and tight threaded connection. Consequently, a back-up tong arrangement is utilized to grip the adjoining tubular member and prevent its rotation in response to the rotational torque being applied to the driven tubular member.
Heretofore, most back-up tongs have utilized a linkage assembly or mechanism to produce a clamping force upon the adjoining tubular member. The disclosures of the following representative U.S. patents depict such clamping arrangements: U.S. Pat. Nos. 2,544,639; 2,705,614; 2,760,392; and 4,082,017.
A draw-back of the back-up tong arrangements utilizing a linkage clamping action is that manual adjustments in the linkage positioning are frequently required to insure that a sufficient clamping force is achieved by the back-up tong. Several adjustments might have to be made in each make up or break out operation in order to achieve the proper clamping force on the adjoining tubular member before the tubular members are fully and tightly threaded together. The clamping linkage position had to be adjusted in each operation to avoid too high a setting which might result in a crushing of the pipe, and yet to arrive at a setting which would sufficiently grip the lower pipe. The prior back-up arrangements did not provide for an automatic increase of the clamping force as the torque through the driving tong increased. Therefore, a setting which adequately secured the adjoining tubular member initially, would frequently be ineffective if additional torque had to be applied to the driven tubular member to continue a threading or unthreading action.
Manual tongs are also used for back-up purposes. However, the bulkiness of these tongs, their weight, and the need to have their operators in the immediate vicinity of the clamping operation, which can be a dangerous environment, are all drawbacks to such devices.
Other power tong back-up assemblies are described in U.S. Pat. Nos. 2,668,689 and 3,025,733. These references also call for the transmission of varying levels of power or torque to the back-up tong in order that the back-up tong might sufficiently grip the adjoining tubular member throughout a threading or unthreading operation.
Consequently, there is believed to have been a need for a power tong and back-up tong assembly which is safe, relatively simple and reliable in construction, and yet effectively operable with a minimum amount of energy needing to be generated and transmitted to the back-up tong of the assembly in order to grip a tubular member during a threading or unthreading operation.